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Abstract:

A sound absorbing structure includes multiple sound absorbers. The sound
absorbers are assembled together into a sound absorbing member. The sound
absorbing member absorbs sound emitted from a sound source. Each of the
sound absorbers is shaped like a hollow tube. Each of the sound absorbers
has a hole extending in its axis direction.

Claims:

1. A sound absorbing structure comprising: a plurality of sound absorbers
assembled together into a sound absorbing member configured to absorb
sound emitted from a sound source, wherein each sound absorber has a hole
extending in an axis direction thereof.

2. The sound absorbing structure according to claim 1, wherein each sound
absorber has a tube shape with a predetermined inner diameter.

3. The sound absorbing structure according to claim 1, wherein the
plurality of sound absorbers are arranged in parallel to each other in a
traveling direction of the sound so that the axis direction of each sound
absorber is perpendicular to the traveling direction of the sound.

4. The sound absorbing structure according to claim 1, wherein each sound
absorber has at least one open end in the axis direction.

5. The sound absorbing structure according to claim 1, further
comprising: a tube-shaped duct body having a wall defining a passage
where the sound travels, wherein the sound absorbing member is attached
to the wall of the duct body.

6. The sound absorbing structure according to claim 5, wherein the axis
direction is inclined at a predetermined angle with respect to the wall
of the duct body.

7. The sound absorbing structure according to claim 1, wherein the axis
direction is inclined at a predetermined angle with respect to a
traveling direction of the sound.

8. A sound absorbing structure comprising: a porous sound absorber
configured to absorb sound emitted from a sound source, wherein the
porous sound absorber has a plurality of holes extending in an axis
direction thereof.

9. The sound absorbing structure according to claim 8, wherein the
plurality of holes extend parallel to each other.

10. The sound absorbing structure according to claim 8, wherein each hole
has at least one open end in the axis direction.

11. The sound absorbing structure according to claim 8, further
comprising: a tube-shaped duct body having a wall defining a passage
where the sound travels, wherein the porous sound absorber is attached to
the wall of the duct body.

12. The sound absorbing structure according to claim 11, wherein the axis
direction is inclined at a predetermined angle with respect to the wall
of the duct body.

13. The sound absorbing structure according to claim 8, wherein the axis
direction is inclined at a predetermined angle with respect to a
traveling direction of the sound.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on Japanese Patent Application No.
2011-150104 filed on Jul. 6, 2011, the disclosure of which is
incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to a sound absorbing structure
having multiple narrow tube-shaped sound absorbers assembled together
into a sound absorbing member or having a porous sound absorber with
multiple holes.

BACKGROUND

[0003] In a sound absorbing structure disclosed in US2005/0067220
corresponding to JP-2005-84693A, multiple Helmholtz resonators (i.e.,
resonant silencers) having different resonant frequencies are arranged to
obtain a sound absorption characteristic over a wide frequency range.

[0004] Specifically, as shown in FIG. 6, the sound absorbing structure
includes an inner member 101 and an outer member 102 that surrounds the
inner member 101.

[0005] The inner member 101 defines an inner wall 104 having openings 103.
The outer member 102 defines an outer wall 105 that extends along the
inner wall 104 of the inner member 101.

[0006] The outer wall 105 forms bellows 106 to improve the sound
absorption characteristic and flexibility of the sound absorbing
structure. The bellows 106 and the inner wall 104 define cavities 107.
The openings 103 of the inner wall 104 are open to the cavities 107.

[0007] A resonator, which is used in the conventional sound absorbing
structure, is a device designed to absorb sound of a specific frequency.
Therefore, to obtain sound absorption characteristics over a wide
frequency range, a lot of resonators having different resonant
frequencies are needed. As a result, the size of the sound absorbing
structure is increased.

[0008] The present inventors have conducted an experiment to evaluate the
effect of the conventional sound absorbing structure to reduce intake
noise. In the experiment, a speaker was placed at one end of the inner
member 101, and a microphone was placed at the other end of the inner
member 101. Then, white noise was generated from the speaker, and sound
caught by the microphone was analyzed by using a fast Fourier transform
(FFT) analyzer. FIG. 7 shows a result of the experiment. As can be seen
from FIG. 7, the sound absorption characteristic of the conventional
sound absorbing structure has an excessive frequency region where the
noise is excessively (i.e., unnecessarily) absorbed. Further, the sound
absorption characteristic has a worse frequency region near the excessive
frequency region. In the worse region, the noise is increased rather than
reduced.

SUMMARY

[0009] In view of the above, it is an object of the present disclosure to
provide a relatively small sound absorbing structure having good sound
absorption characteristics over a wide frequency range.

[0010] According to an aspect of the present disclosure, a sound absorbing
structure includes multiple sound absorbers. The sound absorbers are
assembled together into a sound absorbing member for absorbing sound
emitted from a sound source. Each sound absorber has a hole extending in
its axis direction.

[0011] According to another aspect of the present disclosure, a sound
absorbing structure includes a porous sound absorber for absorbing sound
emitted from a sound source. The porous sound absorber has multiple holes
extending in its axis direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features and advantages of the present
disclosure will become more apparent from the following detailed
description made with reference to the accompanying drawings. In the
drawings:

[0013]FIG. 1 is a diagram illustrating an engine control system according
a first embodiment of the present disclosure;

[0014]FIG. 2 is a diagram illustrating a perspective view of part of an
intake duct used in the engine control system;

[0015]FIG. 3 is a graph showing a relationship between a sound absorption
characteristic and a ratio of a length to an inner diameter of a hollow
absorber of the intake duct;

[0016]FIG. 4 is a diagram illustrating a perspective view of an intake
duct according to a second embodiment of the present disclosure;

[0017]FIG. 5 is a diagram illustrating a partial cross-sectional view of
FIG. 4;

[0018]FIG. 6 is a diagram illustrating a cross-sectional view of a
conventional sound absorbing structure; and

[0019]FIG. 7 is a graph showing a relationship between a sound frequency
and a sound absorption characteristic of the conventional sound absorbing
structure.

DETAILED DESCRIPTION

First Embodiment

[0020] A first embodiment of the present disclosure is described below
with reference to FIGS. 1-3. FIG. 1 shows an engine control system. FIG.
2 shows part of an intake duct (i.e., sound absorbing structure).

[0021] The engine control system includes a turbocharger and an intake air
silencer. The turbocharger compresses intake air by using pressure of
exhaust gas of an internal combustion engine E. The intake air silencer
absorbs intake air noise generated in an intake pipe of the engine E. The
engine control system controls intake air supplied to a combustion
chamber of each cylinder of the engine E.

[0022] The intake air silencer has an intake duct 1 serving as a sound
absorbing structure. The intake duct 1 defines an intake passage R (refer
to FIG. 4) where intake air flowing out of a compressor of the
turbocharger flows.

[0023] As shown in FIGS. 1 and 2, the intake duct 1 has a rectangular
tube-shaped duct body 2 and multiple hollow sound absorbers 4. Noise
emitted from the compressor (i.e., sound source) is transmitted through
the duct body 2. The sound absorbers 4 are made of synthetic resin and
assembled together into a sound absorbing member. The sound absorbing
member is attached to an inner surface of a duct wall 3 of the duct body
2 and exposed to the intake passage R so that the noise emitted from the
compressor can be absorbed by the sound absorbing member. The intake
passage R is defined by the inner surface of the duct wall 3 of the duct
body 2. The sound absorbing member is directly attached to a
predetermined portion of the inner surface of the duct wall 3 by an
adhesive or the like. Alternatively, the sound absorbing member can be
attached to a plate member, and the plate member can be attached to the
predetermined portion of the inner surface of the duct wall 3.

[0024] Each sound absorber 4 has a circular through hole 5 extending
straightly in its axis direction. The sound absorbers 4 are assembled
together into the sound absorbing member in such a manner that a
clearance (i.e., hole) 6 is formed between adjacent sound absorbers 4.
The details of the intake air silencer, in particular, the intake duct 1,
are described later.

[0025] The engine E includes, but is not limited to, a multicylinder
gasoline with multiple cylinders. For example, the engine E can be
multicylinder diesel engine with multiple cylinders.

[0026] The engine E is installed in an engine room of a vehicle together
with the turbocharger. Each cylinder of the engine E is provided with an
injector for injecting fuel into a corresponding intake port at an
optimum time.

[0027] The engine E has an intake pipe and an exhaust pipe. The intake
pipe defines an intake passage where intake air drawn into the combustion
chamber of each cylinder flows. The exhaust pipe defines an exhaust
passage through which exhaust gas flowing out of the combustion chamber
of each cylinder is discharged to the outside.

[0028] The intake pipe is provided with the intake duct 1, an air cleaner
7, the compressor of the turbocharger, an intercooler 8, an electronic
throttle unit, and an intake manifold. The intake manifold is connected
to the intake port of each cylinder of the engine E.

[0029] The exhaust pipe is provided with an exhaust manifold, a turbine of
the turbocharger, an exhaust gas cleaner (i.e., catalyst), and a muffler
9 serving as an exhaust silencer. The exhaust manifold is connected to an
exhaust port of each cylinder of the engine E.

[0030] The air cleaner 7 has a filter for filtering the outside air drawn
into an air introduction passage from an outside air inlet located at an
upstream end of an inlet duct (i.e., outside air introduction duct).

[0031] An outlet of the air cleaner 7 is connected to a compressor housing
of the turbocharger through an intake duct defining an intake passage
where the intake air passing through the air cleaner 7 flows.

[0032] An outlet of the compressor housing is connected to the intercooler
8 through the intake duct 1, which defines the intake passage R where the
intake air flowing out of the compressor of the turbocharger flows.

[0033] The intercooler 8 includes a cooler housing and a cooler core
accommodated in the cooler housing. The cooler core cools the hot intake
air compressed by the compressor of the turbocharger by exchanging heat
between the intake air and a coolant such as cooling liquid or gas.

[0034] An outlet of the intercooler 8 is connected to a throttle body 11
of the electronic throttle unit through an intake duct (i.e., air
connector, air hose) defining an intake duct where the intake air passing
through the cooler core flows.

[0035] The electronic throttle unit includes the throttle body 11, a
throttle valve 12, and an electric actuator 13. The throttle valve 12 is
opened and closed adjust the flow rate of the intake air.

[0036] The throttle valve 12 is supported by a shaft 14. The electric
actuator 13 rotates the shaft 14. The electric actuator 13 has a motor
for opening and closing the throttle valve 12 and a deceleration
mechanism for decelerating rotation of the motor and for transferring the
decelerated rotation to the shaft 14. The motor is electrically connected
to a battery of the vehicle through a motor drive circuit of an engine
electronic control unit (ECU).

[0037] The intake manifold includes a surge tank for reducing a change in
pressure of the intake air flowing from an outlet of the throttle body 11
and intake blanch pipes, each of which is connected to a corresponding
intake outlet of the surge tank.

[0038] The surge tank has a surge tank room for temporarily storing the
intake air and for distributing the intake air between the intake blanch
pipes, each of which is connected to a corresponding combustion chamber
and intake port of each cylinder of the engine E. In FIG. 1, the surge
tank is not shown.

[0039] Each intake pipe branches from the surge tank room and is connected
to the corresponding combustion chamber and intake port of each cylinder
of the engine E. Each intake blanch pipe has an intake blanch passage for
introducing the intake air to the intake port of each cylinder of the
engine E.

[0040] The turbocharger has the compressor and a turbine. The compressor
is located at a point in the intake pipe of the engine E. The turbine is
located at a point in the exhaust pipe of the engine E. In the
turbocharger, the intake air flowing through the intake pipe is
compressed by the compressor, and the compressed air is supplied to the
combustion chamber of each cylinder of the engine E.

[0041] When a turbine wheel 15 of the turbine is rotated by exhaust gas, a
turbine shaft 16 and a compressor impeller 17 that are connected to the
turbine wheel 15 rotates so that the intake air can be compressed by the
compressor impeller 17.

[0042] The turbine includes the turbine wheel 15 and the turbine housing.
The turbine wheel 15 has turbine blades arranged in a circumferential
direction of the turbine wheel 15 and is rotated by pressure of the
exhaust gas of the engine E. The turbine wheel 15 is connected through
the turbine shaft 16 to the compressor impeller 17 to directly rotate the
compressor impeller 17. A wheel accommodation space is formed in the
center of the turbine housing. The turbine wheel 15 is rotatably held in
the wheel accommodation space of the turbine housing.

[0043] Further, a turbine inlet passage and a turbine outlet passage are
formed in the turbine housing. The turbine inlet passage leads the
exhaust gas flowing from a confluence of the exhaust manifold to the
wheel accommodation space. The turbine outlet passage leads the exhaust
gas flowing from the wheel accommodation space to the exhaust gas
cleaner.

[0044] The compressor includes the compressor impeller 17 and the
compressor housing. The compressor impeller 17 has impeller blades
arranged in a circumferential direction of the compressor impeller 17.
The compressor impeller 17 is connected through the turbine shaft 16 to
the turbine wheel 15 and directly rotated by the turbine wheel 15.

[0045] An impeller accommodation space is formed in the center of the
compressor housing. The compressor impeller 17 is rotatably held in the
impeller accommodation space of the compressor housing.

[0046] Further, a compressor inlet passage and a compressor outlet passage
are formed in the compressor housing. The compressor inlet passage leads
the intake gas flowing from the air cleaner 7 to the impeller
accommodation space. The compressor outlet passage leads the intake gas
flowing from the impeller accommodation space to the, intercooler 8
through the intake duct 1.

[0047] An engine body (i.e., cylinder block and cylinder head) of the
engine E has the intake ports opened and closed by an intake valve 21 and
the exhaust ports opened and closed by an exhaust valve 22.

[0048] When the engine E is a gasoline engine, the cylinder head of the
engine E is provided with a spark plug 23 having a tip portion exposed to
the chamber of each cylinder.

[0049] When the engine E is a four-cylinder engine, four combustion
chambers (i.e., cylinder bores) are arranged in the cylinder block of the
engine E in a direction in which the cylinders are arranged. A piston 24
connected through a connecting bar to a crank shaft is supported in each
cylinder bore so that the piston 24 can slidably reciprocate in the
cylinder bore.

[0050] The intake air silencer, in particular, the intake duct 1 according
to the first embodiment is described in detail below with reference to
FIGS. 1-3.

[0051] The intake duct 1 defines the intake passage R where the intake air
flowing out of the compressor of the turbocharger flows.

[0052] Since the intake air is compressed by the compressor impeller 17,
the intake air flowing out of the compressor is at high pressure.
Therefore, it is preferable that the intake duct 1 should absorb sound
over a wide range of high frequencies (e.g., from 1 kHz to 4 kHz).

[0053] As mentioned previously, the intake duct 1 is configured as a sound
absorbing structure having a sound absorbing member for absorbing noise
emitted from the compressor of the turbocharger (i.e., sound on the
downstream side of the compressor). The intake duct 1 includes the
rectangular tube-shaped duct body 2 and multiple hollow sound absorbers
4. The sound absorbers 4 are assembled together into the sound absorbing
member.

[0054] The duct body 2 has a rectangular cross-section perpendicular to
its axis. For example, the duct body 2 can be a single piece of synthetic
resin (i.e., heat-resistant resin) such as polyamide (PA), polyphenylene
sulfide (PPS), polypropylene (PP), or polybutylene terephthalate (PBT).

[0055] An upstream end of the duct body 2 in the intake air flow direction
(i.e., inlet of the intake duct 1) is connected to the outlet of the
compressor housing of the turbocharger. A downstream end of the duct body
2 in the intake air flow direction (i.e., outlet of the intake duct 1) is
connected to an inlet of the intercooler 8.

[0056] The duct wall 3 of the duct body 2 extends parallel to a traveling
direction of the noise emitted from the compressor.

[0057] Each sound absorber 4 is a circular tube having a circular
cross-section perpendicular to its axis. The sound absorbers 4 are made
of synthetic resin (i.e., heat resistant resin) and integrated as a
single piece. Alternatively, the sound absorbers 4 can be separate
pieces. For example, each sound absorber 4 can be made of polyamide (PA),
polyphenylene sulfide (PPS), polypropylene (PP), or polybutylene
terephthalate (PBT).

[0058] For example, the sound absorber 4 can be a narrow straight tube
having the hole 5 with a diameter of 1mm or less. The sound absorbers 4
are attached to the inner surface of the duct wall 3 of the duct body 2
and arranged in parallel to each other in the traveling direction of the
noise emitted from the compressor so that the axis direction of each
sound absorber 4 can be perpendicular to the traveling direction of the
noise.

[0059] Each sound absorber 4 has at least one open end in the axis
direction so that the open end can be perpendicular to the traveling
direction of the noise emitted from the compressor.

[0060] As described in detail later, a sound absorbing characteristic of
the sound absorber 4 depends on a ratio L/φd of a length L (mm) of
the sound absorber 4 in the axis direction to a diameter φd (mm) of
the hole 5 of the sound absorber 4. For example, as the ratio L/φd is
increased, an average amount of sound absorbed by the sound absorber 4 is
increased.

[0061] Next, an operation of the engine control system is described below
with reference to FIGS. 1-3.

[0062] The exhaust gas, discharged from the combustion chamber of each
cylinder of the engine E to the exhaust manifold, flows into the wheel
accommodation space through the turbine inlet passage as an inlet of the
turbine housing of the turbocharger so that the turbine wheel 15 can
rotate. Then, the exhaust gas flows out of the turbine outlet passage as
an outlet of the turbine housing.

[0063] The rotation of the turbine wheel 15 is transferred through the
turbine shaft 16 to the compressor impeller 17 of the compressor so that
the compressor impeller 17 can rotate.

[0064] The intake air, drawn into the intake passage from the air cleaner
7, flows into the impeller accommodation space through the compressor
inlet passage as an inlet of the compressor housing. The intake air
flowing into the impeller accommodation space is compressed by the
compressor impeller 17 rotating with the turbine wheel 15 so that
pressure of the intake air can be increased. The compressed intake air
flows from the compressor outlet passage of the compressor housing to the
intercooler 8 through the intake passage R of the duct body 2 of the
intake duct 1 and is cooled by the intercooler 8. The cooled intake air
flows out of the cooler core of the intercooler 8 and is drawn into the
intake port and the combustion chamber of each cylinder of the engine E
through a throttle bore of the throttle body 11 and the intake blanch
passage of the intake manifold.

[0065] As described above, according to the first embodiment, the intake
duct 1 includes multiple hollow sound absorbers 4. The sound absorbers 4
are assembled together into a sound absorbing member for absorbing sound
emitted from a sound source such as the compressor. Each sound absorber 4
is tube-shaped and has the hole 5 with a predetermined diameter, for
example, 1mm or less. The intake duct 1 is connected to the outlet of the
compressor housing of the turbocharger. The sound absorbing member is
installed inside the duct body 2 and exposed to the intake passage R
where the intake air flowing out of the compressor flows. Specifically,
the sound absorbing member is attached to the inner surface of the duct
wall 3 that defines the intake passage R.

[0066] The sound absorber 4 is made of synthetic resin. Sound (i.e.,
noise) entering the hole 5 of the sound absorber 4 hits against an inner
wall of the sound absorber 4 so that energy of the sound can be damped.
Further, the energy of the sound can be damped by the vibration of the
air in the hole 5 of the sound absorber 4.

[0067] A desired sound absorption characteristic of the sound absorber 4
can be obtained by adjusting the specifications of the sound absorber 4.
For example, the desired sound absorption characteristic can be obtained
by adjusting the ratio L/φd of the length L of the sound absorber 4
in the axis direction to the diameter φd of the sound absorber 4.

[0068] According to the first embodiment, each sound absorber has the same
ratio L/φd. Alternatively, for example, the sound absorbers 4 can be
divided into a first group and a second group. In this case, each of the
sound absorbers 4 of the first group can have a first ratio L/φd, and
each of the sound absorbers 4 of the second group can have a second ratio
L/φd different from the first ratio L/φd. In such an approach,
the sound absorbing member constructed with the sound absorbers 4 having
different ratios L/φd can absorb noise over a wide frequency range.

[0069] As mentioned above, it is preferable that the intake duct 1 should
absorb sound over a high frequency range from 1 kHz to 4 kHz to absorb
the noise emitted from the compressor of the turbocharger. FIG. 3 is a
graph illustrating a relationship between the ratio L/φd and the
average amount of sound absorbed by the sound absorber 4. As can be seen
from FIG. 3, the average sound absorption amount of 15 dB over the
frequency range from 1 kHz to 4 kHz can be obtained by adjusting the
ratio L/φd to 33.8 or more. For example, when the length L is 10 mm,
the ratio L/φd of 33.8 or more can be obtained by adjusting the
diameter φd to a value less than 0.3 mm.

[0070] Thus, the sound absorbing structure according to the first
embodiment intake can exhibit high sound absorption performance over a
wide frequency range, although the intake duct 1 has a relatively small
size and does not require a large mounting space. In particular, the
sound absorbing structure can effectively absorb noise over a wide range
of high frequencies. Further, unlike the conventional sound absorbing
structure, the sound absorbing structure can have a sound absorption
characteristic without a worse frequency region where noise is increased
rather than reduced.

[0071] A fiber assembly, such as a felt, a fiberglass, or glass wool, or a
porous absorber such as a thin film, a non-woven fabric, or a urethane
foam can be used as a sound absorbing member for absorbing noise emitted
from a sound source. For example, the fiber assembly or the porous
absorber is used as an insulator mounted on a floor of a vehicle.
Generally, the fiber assembly or the porous absorber has flexibility.
Therefore, assuming that such a fiber assembly or a porous absorber is
used as a sound absorbing member mounted in an intake duct of an engine
in order to absorb intake noise emitted from the engine or a
turbocharger, the sound absorbing member is largely deformed by intake
pulsation due to a change in pressure in the intake duct. As a result, a
clearance or hole in the sound absorbing member may be widened or
narrowed, and sound absorption characteristic of the sound absorbing
member may be deteriorated.

[0072] For example, according to the first embodiment, narrow tube-shaped
sound absorbers 4, each having the hole 5 with the diameter of 1mm or
less, are assembled together into the sound absorbing member. In such an
approach, it is less likely that the sound absorbers 4 are deformed by
the pressure change. Therefore, the sound absorbing structure can
maintain its sound absorption characteristic.

[0073] Since the sound absorbing member is attached to the inner surface
of the duct wall 3 of the intake duct 1 by an adhesive or the like, the
intake duct 1 can be reinforced by the sound absorbing member.
Accordingly, the intake duct 1, which is connected to the outlet of the
compressor housing of the turbocharger, can withstand the pressure
compressed by the compressor of the turbocharger even when the thickness
of the duct wall 3 of the duct body 2 is reduced.

[0074] Since the sound absorbing member is located inside the duct body 2,
the intake duct 1 can have a small size and does not require a large
mounting space. Therefore, the intake duct 1 can be easily mounted in a
vehicle, for example, in an engine room without increasing the size of
the engine room.

[0075] According to the first embodiment, the clearance 6 is formed
between adjacent sound absorbers 4. Since the clearance 6 can absorb
noise emitted from a sound source such as the compressor, the sound
absorbing characteristic of the sound absorbing structure can be
improved. Alternatively, the clearance 6 can be filled with, for example,
synthetic resin.

[0076] According to the first embodiment, the sound absorbing member is
directly attached to the inner surface of the duct wall 3. Alternatively,
the sound absorbing member can be accommodated in a tube-shaped housing,
and then the housing can be attached to the inner surface of the duct
wall 3.

Second Embodiment

[0077] An intake duct 1 according to a second embodiment of the present
disclosure is described below with reference to FIGS. 4 and 5. A
difference of the second embodiment from the first embodiment is as
follows.

[0078] Like the first embodiment, the intake duct 1 as a sound absorbing
structure includes multiple hollow sound absorbers 4 that are made of
synthetic resin and assembled together into a sound absorbing member. The
sound absorbing member is attached to the inner surface of the duct wall
3, which defines the intake passage R of the duct body 2, by using an
adhesive or the like.

[0079] Each sound absorber 4 is a circular tube having a circular
cross-section perpendicular to its axis. The sound absorbers 4 are made
of synthetic resin and integrated together. For example, the sound
absorber 4 can be a narrow straight tube having an inner hole 5 with a
diameter of 1mm or less.

[0080] The sound absorbing member is attached to the inner surface of the
duct wall 3 of the duct body 2 in such a manner that the axes of the
sound absorbers 4 are parallel to each other.

[0081] The sound absorber 4 has at least one open end in its axis
direction.

[0082] The axes of the sound absorbers 4 are inclined in a direction
toward (or away from) the compressor of the turbocharger at a
predetermined angle θ with respect to the inner surface of the duct
wall 3 of the duct body 2.

[0083] That is, the axes of the sound absorbers 4 are inclined in the
direction toward (or away from) the compressor of the turbocharger at the
predetermined angle θ with respect to the traveling direction of
noise emitted from the compressor.

[0084] As described above, according to the second embodiment, the axes of
the sound absorbers 4 of the sound absorbing member are inclined in the
direction toward (or away from) the compressor of the turbocharger at the
predetermined angle θ with respect to the inner surface of the duct
wall 3 of the duct body 2. In such an approach, the sound absorbing
member can effectively absorb a progressive wave of the noise emitted
from the compressor. Thus, noise leaking out of the duct body 2 can be
reduced rapidly.

[0085] In this case, the sound absorbing member may not effectively absorb
a reflection wave of the noise emitted from the compressor. However, the
refection wave is reduced with a reduction in the progressive wave.
Therefore, the noise leaking out of the duct body 2 can be reduced by
reducing the progressive wave of the noise.

[0086] Specifically, as shown in FIG. 5, when the axes of the sound
absorbers 4 of the sound absorbing member are inclined in the direction
toward a sound source, from which a sound D1 is emitted, at the angle
with respect to the inner surface of the duct wall 3 of the duct body 2,
it is likely that the sound absorbing member absorbs the sound D1. In
contrast, when the axes of the sound absorbers 4 of the sound absorbing
member are inclined in the direction away from a sound source, from which
a sound D2 is emitted, at the angle θ with respect to the inner
surface of the duct wall 3 of the duct body 2, it is less likely that the
sound absorbing member absorb the sound D2.

[0087] Since the axes of the sound absorbers 4 of the sound absorbing
member are inclined at the angle θ with respect to the inner
surface of the duct wall 3 of the duct body 2, the thickness of the sound
absorbing member is reduced so that the size of the intake duct 1 can be
reduced. Thus, the intake duct 1 can be easily mounded in an engine room
of the vehicle.

[0088] Further, according to the second embodiment, as shown in FIG. 4, a
clearance 6 is formed between adjacent sound absorbers 4. Since the
clearance 6 can absorb noise emitted from a sound source such as the
compressor, the sound absorbing characteristic of the sound absorbing
member can be improved. Alternatively, the clearance 6 can be filled
with, for example, synthetic resin.

[0089] Further, according to the second embodiment, the sound absorbing
member is directly attached to the inner surface of the duct wall 3.
Alternatively, the sound absorbing member can be accommodated in a
tube-shaped housing, and then the housing can be attached to the inner
surface of the duct wall 3.

[0090] (Modifications)

[0091] While the present disclosure has been described with reference to
embodiments thereof, it is to be understood that the disclosure is not
limited to the embodiments and constructions. The present disclosure is
intended to cover various modification and equivalent arrangements. In
addition, while the various combinations and configurations, other
combinations and configurations, including more, less or only a single
element, are also within the spirit and scope of the present disclosure.

[0092] In the embodiments, as shown in FIG. 1, the intake duct 1 is
located on the downstream side of the compressor impeller 17. That is,
the intake duct 1 is located between the compressor impeller 17 and the
intercooler 8. Alternatively, the intake duct 1 can be located on the
upstream side of the compressor impeller 17. That is, the intake duct 1
can be located between the compressor impeller 17 and the air cleaner 7.

[0093] In the embodiments, the sound absorber 4 is a circular tube having
a circular cross-section perpendicular to its axis. The sound absorber 4
is not limited to such a circular tube. For example, the sound absorber 4
can be a rectangular or hexagonal tube having rectangular or hexagonal
cross-section perpendicular to its axis.

[0094] In the embodiments, both ends of the sound absorber 4 in its axis
direction are opened. Alternatively, one end of the sound absorber 4 in
its axis direction can be closed.

[0095] In the embodiments, the shape and size of one end of the sound
absorber 4 is the same as the shape and size of the other end of the
sound absorber 4 in its axis direction. That is, the hole 5 of the sound
absorber 4 has a uniform diameter. Alternatively, at least one of the
shape and size of one end of the sound absorber 4 can be different from
the shape and size of the other end of the sound absorber 4 in its axis
direction. That is, the hole 5 of the sound absorber 4 can have a
non-uniform diameter.

[0096] The sound absorber 4 can have a curved or bent tube shape instead
of a straight tube shape.

[0097] In the embodiments, the sound absorber 4 is made of synthetic
resin. Alternatively, the sound absorber 4 can be made of a material
other than synthetic resin.

[0098] For example, the sound absorber 4 can be formed by punching a hole
in a solid base. Alternatively, the sound absorber 4 can be formed by
melting a fiber or the like contained in a solid base.

[0099] In the embodiments, multiple hollow sound absorbers 4 are assembled
together into a sound absorbing member. Alternatively, a porous sound
absorber having multiple holes extending in its axis direction can be
employed as a sound absorbing member.

[0100] For example, the porous sound absorber can be a thin film, a
non-woven fabric, or a urethane foam. Alternatively, the porous sound
absorber of the second embodiment can be formed by filling the clearance
6 of the sound absorbing member of the first embodiment with the same
material as the sound absorber 4.

[0101] A porous sound absorber made of resin and a porous sound absorber
made of metal can be assembled together into a single porous sound
absorber.

[0102] The holes of the porous sound absorber can extend parallel to each
other in a traveling direction of sound emitted from a sound source.

[0103] Each hole of the porous sound absorber can have at least one open
end in its axis direction.

[0104] The porous sound absorber can be attached to the inner surface of
the duct wall 3 of the duct body 2.

[0105] The axes of the holes of the porous sound absorber can be inclined
in a direction toward (or away from) a sound source at a predetermined
angle θ with respect to the duct wall 3 of the duct body 2 or a
traveling direction of sound emitted from the sound source.

[0106] The sound absorbing structure according to the present disclosure
can be applied to a vehicle part other than the intake duct 1, such as an
air cleaner housing, a surge tank, an intake manifold, a floor, a
ceiling, a wall, a door, a panel, or a hood of the vehicle. Further, the
sound absorbing structure can be applied to an object other than a
vehicle, such as a floor, a ceiling, a wall, a door, a panel, or a hood
of a an the intake duct 1, such as air cleaner housing, a surge tank; or
an intake manifold. Further, the sound absorbing structure can be applied
to a floor, a ceiling, a wall, a door, a panel, a hood of a building with
an acoustic chamber such as a concert hall.

[0107] In the embodiments, the duct body 2 has a straight tube shape.
Alternatively, the duct body 2 can have a curved tube shape. Further, the
duct wall 3 can have a concave or convex surface with a predetermined
curvature radius instead of a flat surface.